In healthy individuals, clearance of mucus from the respiratory tract is accomplished primarily by the body's normal mucociliary action, coupled with coughing. Under normal conditions these mechanisms are very efficient; the mucociliary transport system continually transports a layer of mucus secreted in the lungs up the trachea and out of the respiratory system to be swallowed, while coughing displaces larger blockages. The mucociliary transport system depends upon cilia, small cytoplasmic extensions of cells lining the inside of the respiratory system. Cilia rhythmically move side to side, progressively shifting the layer of mucus to the trachea. Ciliary movement has a predictable rate (the Cilia Beat Frequency (CBF)), which in healthy individuals has a frequency of about 10-30 beats per second. Impairment of the normal mucociliary transport system (slowing the CBF below 10 beats per second) or hypersecretion of respiratory mucus results in an accumulation of mucus and debris in the lungs which may lead to severe medical conditions such as hypoxemia, hypercapnia, chronic bronchitis, and pneumonia. These conditions diminish quality of life, and may even prove fatal. Many medical conditions can produce abnormal respiratory mucus clearance, including pertussis, cystic fibrosis, atelectasis, bronchiectasis, cavitating lung disease, vitamin A deficiency, chronic obstructive pulmonary disease, asthma, and immotile cilia syndrome. Exposure to cigarette smoke, air pollutants, and viral infections also inhibits mucociliary function. Post surgical patients, paralysed persons, and newborns with respiratory distress syndrome also exhibit reduced mucociliary transport. Respiratory system blockages also occur in patients suffering from emphysema, tuberculosis, and disorders caused by many other pathogens which affect the respiratory system.
Chest physiotherapy (CPT) is used to enhance respiratory mucus transport. CPT may include mechanical manipulation of the chest, postural drainage with vibration, directed cough, active cycle of breathing, and autogenic drainage. External manipulation of the chest and respiratory behavioural training are accepted practices according to the American Association for Respiratory Care Guidelines, 1991. CPT involves a caregiver “clapping” or pounding on the chest and back over each lobe of the lungs, coupled with inhalation therapy. A typical CPT session requires half to three-quarters of an hour. While the mechanism by which CPT clears mucus is not entirely clear, the pounding dislodges air way secretions which drain towards the mouth and are removed by active coughing. Various kinds of CPT are often combined by physicians when designing regimes to enhance mucus clearance.
Cystic fibrosis (CF) is one important disorder in which CPT is used to help clear air ways or lungs. Cystic fibrosis (CF) is an inherited life-threatening genetic disease among Caucasians, afflicting about 1 in 600 children. One in twenty five persons of European descent carry the mutation which causes CF. This genetic defect disrupts cellular chloride ion transfer, causing mucus from the exocrine glands to become abnormally thick and sticky, eventually blocking passages within the pancreas, lungs, reproductive organs, and liver. Disruption of the pancreas inhibits enzyme secretion, sometimes resulting in osteoporosis. Thick mucus may block reproductive tracts, in particular lowering male fertility. Crucially, the thick mucus accumulates in the lung's respiratory tracts, causing chronic infections, scarring, and decreased vital capacity. Normal coughing is not sufficient to dislodge these mucus deposits. CF symptoms usually appear during the first 10 years of life, typically in infancy, and significantly reduce life expectancy. However, with advances in digestive enzyme supplementation, anti-inflammatory therapy, chest physical therapy, and antibiotics, the median life expectancy currently exceeds 30 years, and some patients live into their 50's and beyond. While some patient mortality results from severe gastrointestinal disruptions, the majority of CF patients (90 percent) ultimately succumb to respiratory system failure.
Most CF patients use CPT once to four times a day as part of their standard preventative care program to maintain vital capacity and inhibit infection. CPT requires the assistance of a second individual, ideally a nurse or respiratory therapist, but more typically a family member. Effective CPT requires precise pounding, and CPT is exhausting for the CF patient and caregiver. A tired or inaccurate caregiver often only provides incomplete relief. CF patient dependence upon a second individual to perform CPT severely limits the independence of the CF patient. Additionally, pounding involves sharp blows, which can bruise patients, and may even break bones, particularly in small children and CF patients who suffer from osteoporosis.
Over the past several decades, a diverse assortment of devices have attempted to provide an alternative to caregiver delivered CPT for persons suffering from disorders which obstruct lungs or air ways, including CF. CPT replacement devices typically mobilize and clear mucus by creating chest wall oscillations analogous to those experienced by a patient undergoing manual CPT. These devices differ in the kind of force applied and any resulting motion experienced by the subject, and by whether the force is administered locally, over a large area, to the entire chest, or the entire body. Inventions apply force by repeated chest constriction, chest vibration, and impact or blow-like forces (percussion) to the entire patient, or specific locations.
Most marketed devices address lung congestion by pneumatically generated vibrations. These devices are usually large and restrict user mobility, and fail to target the lower lobes of the lungs, the typical infection start point.
Percussion based devices have been described in the literature. Strom et al., in U.S. Pat. No. 4,508,107, discloses a hand-held pneumatic impact system, and Mulligan et al., in U.S. Pat. No. 5,261,394 describe a chest pack containing two reciprocating arms which simultaneously strike the user's chest on either side of the sternum. Percussion based devices possess many of the drawbacks associated with manual CPT therapy, the sharp impacts can injure young or frail patients, and therefore these devices are not suitable in all cases. Furthermore, the strength of the impacts and associated recoil makes manipulation and control of these devices inherently difficult.
A number of commercially available lung clearing devices use constriction, a repeated squeezing and release of the entire chest region. Constriction may be provided by a variety of means. Certain apparatus, such as the commercially available Vest Airway Clearance System (“The Vest™”) distributed by Hill Rom, a subsidiary of Hillenbrand Industries, Inc. (described in Van Brunt et al., U.S. Pat. No. 5,769,797 and numerous other patents) apply pressure to the patient's chest pneumatically. The Vest contains air bladders which are periodically pressurized and depressurized by an external air pressure system, repeatedly squeezing the chest at a frequency of 5-20 Hz. Another vest apparatus with a distinct pneumatic pressure source, operating at 5-25 Hz, is described by Hansen, see for example U.S. Pat. No. 6,547,749. The device described in Van Brunt, U.S. Pat. No. 6,736,785 creates analogous patient body motions via a mechanism cyclically squeezing the subject's chest with an inflexible circumferential chest band. Arbisi et al., in U.S. Pat. No. 5,235,967 describe forces being applied to a subject by repulsion between numerous electromagnets mounted within a flexible vest or shirt like garment, the magnetic repulsion pressing a layer of electromagnets onto the subject. All these apparatus apply force over the entire chest, typically by surrounding the chest in a garment, and then repeatedly squeezing inward. These inventions are often bulky, for example, the pneumatic vests require a large external pressure source. Patients undergoing constriction based therapy often have difficulty breathing due to the way these devices compress the chest.
A wide variety of hand-held vibrators have been described for treating CF patients and other respiratory ailment sufferers. These devices may rhythmically pound the chest at high rates (ex. Denton et al. U.S. Pat. No. 4,079,733, preferably impacting the chest at 115 Hz), move parallel to the surface of the subject (ex. Muchinsky et al., U.S. Pat. No. 4,098,266), or both at once (ex. Muchinsky et al., U.S. Pat. No. 4,102,334). Many of these hand-held units are not particularly portable, and have a large external mechanical power source. Additionally, these hand-held vibrators require an attendant to maintain the device in contact with the patient, and press the vibrator against the patient. Since these devices inherently move and vibrate, the person holding the vibrator must overcome these motions to keep the hand-held vibrator in place, an effort that can be tiring and inconvenient. Larouche et al., in U.S. Pat. No. 5,167,226, discloses a combined clapping and vibrating device where a nominally hand-held device is only practical once mounted on a bed by a supporting arm, presumably to address this problem. With hand-held vibrations, treatment is local and the user must reposition the vibrator from chest area to chest area, resulting in lengthy and potentially incomplete treatment sessions.
Other devices which assist clearing lungs and air ways vibrate the entire subject, or the subject's chest. One strategy involves submerging the subject in a bath, then transmitting vibrations from a source such as a audio speaker to the subject via the fluid (see for example Nedwell, U.S. Pat. No. 6,190,337, Rogers et al., U.S. patent application Ser. No. 2002/0014235, published Feb. 7, 2002). Obviously, these vibrators are large and essentially immobile, and impractical for daily home use. Vibrating beds such as the pneumatic design described in Hand et al. (U.S. patent application Ser. No. 2002/0195144, published Dec. 26, 2002) have similar limitations.
Another approach is to vibrate the air within the patient, rather than the patient's body (see for example Gibson, UK Patent No. 2,196,585, Jam, U.S. patent application Ser. No. 2004/0069304, published Apr. 15, 2004, Benarrouch, et al., U.S. Pat. No. 6,176,235, Fowler-Hawkins, U.S. Pat. No. 6,702,769). One variant of this approach has been marketed by Scandipharm as “The Flutter™”. The Flutter uses the patient's breath to oscillate a ball bearing, creating vibrations which are then transmitted down the patient's air ways. This technique is limited by the strength at which the patient's breath can oscillate the ball bearing, a potentially serious limitation when treating patients suffering from chronic respiratory illness. Furthermore, these techniques transmit vibrations by air, a much less mechanically efficient vibration transmission method than vibration transmission through solids.
There remains a need for a device which adequately provides a replacement for manual CPT, allows patient independence, and provides rapid, efficient, and consistent treatment.